Outside experts to review water quality at North Idaho’s scenic Lake Coeur d’Alene

Years of water-quality data from scenic Lake Coeur d’Alene will be reviewed by a stable of experts starting in 2021.

The data has shown a continued deterioration in the lake’s health and spurred calls for more drastic action to protect the North Idaho gem from pollution.

According to the data, the volume of phosphorus flowing into the lake has roughly doubled since the 1990s. That’s a troubling development for a lake that has roughly 75 million metric tons of sediment polluted with lead and other heavy metals, the toxic legacy of more than a century of mining in Idaho’s Silver Valley.

Those toxins are mostly concentrated in the lake’s sediment, but increased plant growth in the lake, spurred by higher levels of phosphorous, threatens to reduce the lake’s oxygen to a point at which the heavy metals could become resuspended in the lake water.

Some question the validity of the data.

“I have full faith in the data,” said Marie Schmidt, a coordinator for the University of Idaho’s Community Water resource center. “The trends that we’re seeing it go in are worrisome, and I think we need to be doing something about it. But I understand that not everybody has full faith in that data.”

The data has been collected by Coeur d’Alene Tribe, state scientists and the U.S. Environmental Protection Agency.

The review may show the state where additional monitoring is necessary, said Jamie Brunner the Idaho Department of Environmental Quality lake management supervisor. The lake management plan calls for a comprehensive review “in the event that monitoring data reveals trends that approach a trigger level.”

“We need to have some other eyes on this,” Brunner said. “What are the data gaps that we are missing?”

The DEQ, with the support of Kootenai County, has contracted the National Academy of Sciences to analyze more than a decade of available information to determine future water quality conditions in Lake Coeur d’Alene, according to a news release.

The county is contributing $200,000 toward the analysis. The state is contributing $500,000 .

The Coeur d’Alene Tribe is not paying for the study but has endorsed it. The EPA has pledged some financial support, according to the news release.

Human development and logging have led to increased levels of phosphorus and plant growth in the lake, prompting some calls for more strict lakeshore development laws.

Kootenai County regulations include a 25-foot shoreline protection buffer prohibiting removal of native vegetation, site disturbance or building a structure other than stairs or docks. The ordinance has not been modified since 1973, according to the Coeur d’Alene Press.

Oxygenated water acts like a cap on the metals, keeping them locked in the sediment. At the same time, a warming climate will increase the likelihood of those metals resuspending as snowpack levels decrease and water temperatures rise during the summer months.

Last year, frustrated by the apparent lack of action to protect the lake, the Coeur d’Alene Tribe withdrew from the lake management plan. The tribe did not immediately return a call for comment.

Nominations for reviewers have already been accepted by the NAS. By late January, once the NAS has narrowed nominees down, a draft panel will be announced, and the public will have three weeks to comment.

Reviewers will examine the available data focusing broadly on the “near-term risk of toxic metals release.” They will not collect any additional data. The final report is expected in the summer of 2022.

“I think it’s just prudent to have experts from across the country to look at it to make sure,” Brunner said.

This is not the first time Coeur d’Alene Lake data has been reviewed by a third party.

In 2005, the NAS published a massive report finding that the EPA’s cleanup plan for the Silver Valley was based on “generally sound” scientific and technical principles and that the agency ought to expand its effort to protect residents and wildlife in the basin.

Lake Coeur d’Alene is included in the federal Superfund site in the Silver Valley but does not receive Superfund money. Instead, the state of Idaho and the Coeur d’Alene Tribe were given water-quality management authority by the federal government.

This story was originally published January 2, 2021 at 5:00 AM.